Ship bottoms, underwater structures, fishing nets and the like are likely to have their appearance and function damaged by the adhesion to surface and propagation of various aquatic organisms including animals such as shellfishes and barnacles, seaweeds such as layer and bacteria caused when they are exposed to the water for a prolonged period of time.
In particular, when the above aquatic organism adheres to a ship's bottom and propagates, the danger is highly probable that the roughness of the entire surface of the ship is increased to thereby lower the speed of the ship and increase the fuel consumed by the ship. Removing the aquatic organism from the ship bottom necessitates spending of much labor and working time at a dock. Further, when bacteria adhere to, for example, an underwater structure and propagates to thereby cause adhesion of slime (sludgy matter), there is the danger that the slime putrefies to thereby cause damages such as deterioration of the properties of the underwater structure and thus marked shortening of the life thereof.
For example, a composition comprising a copolymer of tributyltin methacrylate and methyl methacrylate and cuprous oxide (Cu.sub.2 O) has been used as an antifouling paint effectively applicable to ship bottoms for enabling the prevention of the above damages. This copolymer of the antifouling paint is hydrolyzed in the seawater to thereby liberate organotin compounds such as bistributyltin oxide (tributyltin ether of the formula Bu.sub.3 Sn--O--SnBu.sub.3 wherein Bu is a butyl group) and tributyltin halides (Bu.sub.3 SnX wherein X is a halogen atom), so that antifouling effect is exerted. Moreover, the copolymer hydrolyzate per se is a hydrolyzable self-polishing paint which is water-soluble and thus is dissolved in the seawater, so that no resin residue is left on the surface of the ship bottom coating to thereby enable continually maintaining active surface.
However, the above organotin compounds are so highly toxic that apprehensions are being entertained with respect to marine pollution, occurrence of anomalous fish and adverse effects on ecosystem through food chain. Therefore, the development of an antifouling paint not containing tin is desired as a substitute therefor.
For example, antifouling paints based on silyl esters as described in Japanese Patent Laid-open Publication Nos. 4(1992)-264170, 4(l992)-264169 and 4(1992)-264168 can be mentioned as the above antifouling paint not containing tin. However, these antifouling paints have problems that not only are their antifouling capabilities poor but also cracking and peeling are likely to occur as pointed out in Japanese Patent Laid-open Publication Nos. 6(1994)-157941 and 6(1994)-157940.
Further, Japanese Patent Laid-open Publication No. 2(1990)-196869 teaches an antifouling paint comprising a copolymer with blocked acid functionality (A) which is obtained by copolymerizing trimethylsilyl methacrylate, ethyl methacrylate and methoxyethyl acrylate in the presence of an azo initiator and which contains carboxyl groups blocked with trimethylsilyl groups and a polyvalent cation compound (B). Also, an antifouling paint comprising a chlorinated paraffin plasticizer in addition to the above acid-functional copolymer (A) and polyvalent cation compound (B) is disclosed in the Example portion of the publication. However, the coating film obtained from the antifouling paint disclosed in the above Example portion has a drawback in that the cracking resistance thereof is not fully satisfactory. That is, in Japanese Patent Laid-open Publication No. 2(1990)-196869, there is no description teaching what antifouling paint is excellent in cracking resistance and storage stability, especially, cracking resistance.
Published Japanese Translation of PCT Patent Applications from Other States, No. 60(1985)-500452 and Japanese Patent Laid-open Publication No. 63(1988)-215780 describe a resin for antifouling paint which is obtained by copolymerizing a vinyl monomer having an organosilyl group, such as a trialkylsilyl ester of (meth)acrylic acid, with another vinyl monomer and which has a number average molecular weight of 3000 to 40,000 and further describe that the resin can be blended with an organic water binder such as trimethyl orthoformate, an antifouling agent such as cuprous oxide and a pigment such as red iron oxide. However, as described in Japanese Patent Laid-open Publication No. 6(1994)-157940, this resin for antifouling paint has drawbacks in that it is likely to gel during the storage thereof and that the coating film formed from the antifouling paint is poor in cracking and peeling resistances.
Japanese Patent Publication No. 5(1993)-32433 corresponding to the above Published Japanese Translation of PCT Patent Applications from Other States, No. 60(1985)-500452 discloses an antifouling paint comprising a poison (a) and a polymer binder (b) having a repeating unit of the formula (--CH.sub.2 --CXCOOR)--(B)-- wherein X is H or CH.sub.3, R is SiR'.sub.3 or Si(OR').sub.3 in which R' is an alkyl group, etc. and B is an ethylenically unsaturated monomer residue, which polymer binder has a specified hydrolysis rate, and describes that the paint can contain a solvent, a water-sensitive pigment component, an inert pigment, a filler and a retarder. However, the coating film obtained from the antifouling paint described in the publication has a drawback in that its cracking resistance is poor.
Japanese Patent Laid-open Publication No. 7(1995)-18216 discloses a coating composition comprising as principal components an organosilicon-containing polymer (A) having in its molecule a triorganosilicon ester group represented by the formula --COO--SiR.sup.1 R.sup.2 R.sup.3 wherein each of R.sup.1, R.sup.2 and R.sup.3 is, for example, an alkyl group having 1 to 18 carbon atoms and copper or a copper compound (B), which coating composition contains as an essential component other than the components A and B a silicon compound having an alkoxy group (C) represented by the formula: ##STR1##
wherein each of R.sup.4, R.sup.5 and R.sup.6 represents, for example, a hydrogen atom, an alkoxy group or a cycloalkoxy group having 1 to 18 carbon atoms; R.sup.7 represents, for example, an alkyl group having 1 to 18 carbon atoms; and n is an integer of 1 to 3. In the columns describing constitution and function of invention of the publication, it is described that a plasticizer such as a chlorinated paraffin and a resin such as an acrylic resin may be incorporated in the coating composition according to necessity. However, the coating film obtained from the coating composition described in the publication has a drawback in that its cracking resistance is poor. PA1 wherein each of R.sup.1, R.sup.2 and R.sup.3 independently represents a group selected from among alkyl and aryl groups and X represents an acryloyloxy, a methacryloyloxy, a maleoyloxy or a fumaroyloxy group, PA1 and monomer B represented by the formula: PA1 Y--(CH.sub.2 CH.sub.2 O).sub.n --R.sup.4, PA1 wherein R.sup.4 represents an alkyl or an aryl group, Y represents an acryloyloxy or a methacryloyloxy group and n is an integer of 1 to 25.
Japanese Patent Laid-open Publication No. 7(1995)-102193 discloses a coating composition comprising as essential components a copolymer obtained by polymerizing a monomer mixture containing monomer A represented by the formula: ##STR2##
Also, in the antifouling coating film for ships or underwater structures, there is a demand for the development of a self-polishing antifouling coating composition capable of forming a coating film being excellent in cracking and peeling resistances at a zone under alternate dry and wet, for example, a water line zone of ships brought in an environment in which immersion in the seawater and exposure to the air alternate with each other, which coating film can inhibit damages even where high pressure applies, for example, at block parts during ship building.
The present invention has been made with a view toward solving the above problems of the prior art, and an object of the present invention is to provide an antifouling coating composition which not only enables forming an antifouling coating film being excellent in cracking resistance, peeling resistances, antifouling properties and self-polishing (consumability) properties but also is excellent in storage stability.
Other objects of the present invention are to provide a coating film formed from this antifouling coating composition, an antifouling method using the antifouling coating composition and a hull or an underwater structure coated with the above coating film.
A further object of the present invention is to provide an antifouling coating composition capable of forming a coating film being excellent in properties such as cracking and peeling resistances not only in dry atmosphere, for example, above drafts of hulls and underwater structures but also in atmosphere in which immersion in the seawater and exposure to dryness alternate with each other because of draft changes, which coating film has such a high strength that, even if a pressure is applied to the coating film by blocks or the like, the damage by the pressure can be inhibited to a level of practically no significance.